1. Field of the Invention
The present invention relates to a fuel injection control apparatus for an internal combustion engine, and a method for controlling an internal combustion engine.
2. Discussion of the Background
As a fuel injection control apparatus for an internal combustion engine of the related art, the control apparatus disclosed in Japanese Patent No. 3758003 is known. The internal combustion engine disclosed in this publication is a so-called gasoline direct injection engine in which fuel is directly injected into a combustion chamber via a fuel injection valve. The fuel injection control apparatus includes a cooling water temperature sensor, a crank angle sensor, etc. and calculates the engine speed NE on the basis of an output signal from the crank angle sensor.
In this fuel injection control apparatus, as shown in FIG. 2 (steps S14 to S22) and described in paragraphs [0018] to [0028] of Japanese Patent No. 3758003, when the cooling water temperature TW is lower than a predetermined temperature TW0, i.e., when a warm-up operation is being performed, fuel injection is controlled as follows. The amount of fuel to be injected in the intake stroke is first calculated. Then, after a fuel division ratio Υ is set in accordance with the cooling water temperature TW, the injection interval Int is set. Then, the injection completion timing is set in accordance with the engine speed NE. Then, in step S24, fuel is injected twice during the intake stroke, on the basis of the amount of fuel, the fuel division ratio Υ, the injection interval Int, and the injection completion timing. The reason why fuel injection is performed twice is described in paragraphs [0022] and [0023] of Japanese Patent No. 3758003. That is, if fuel injection is performed only once in the intake stroke during the warm-up operation, the fuel injection time becomes longer, which increases the amount by which fuel penetrates into the combustion chamber and causes fuel to adhere to the wall of the combustion chamber. Because of this, the atomization degree is lowered, thereby facilitating the generation of smoke. As described in paragraph [0031] of Japanese Patent No. 3758003, if the cooling water temperature TW is equal to or higher than the predetermined temperature TW0, i.e., if the warm-up operation is not performed, regular fuel injection control is performed in step S26, and fuel is injected only once during the intake stroke.